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Monday, 7 February 2011

We designed a system for wirelessly controlling relays and monitoring current. This is used for a home load simulation. By wirelessly turning relays on and off by sending commands from a PC to a microcontroller we can change the total load (current) to our simulated home.

For wireless communication, we used XBee Series 2 Zigbee RF modules. One of these modules was connected to a microcontroller and the home load simulation, while another was connected to the PC, which was used for collecting and displaying data as well as for relay monitoring and control.

Background Theory:

What we have built is a simple transmission system based on the Zigbee routing and networking protocol. This protocol and its details are discussed in greater detail in the Standards section (below); in this section, we focus on underlying network theory and the role this theory played in our project.

Data networks (and transmission systems) are typically divided into various layers based on functionality. This is sometimes called a “protocol stack” (in our case, we are using a “Zigbee stack”). Essentially, the lower the layer, the closer we are to worrying about actual physical electrons flying around. Conversely, the higher the layer, the less we are worrying about physical constraints and the more abstract the data structures are that we are dealing with and manipulating.

The most famous of these layering models is the Open System Interconnection (OSI) Reference Model, which is shown below: